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Engineers Perform Computational Logic with Optical and Electrical Signals

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In work that could help advance the development of low-power, high-performance computer chips, researchers at the University of Tokyo and RIKEN have employed UV light and electric fields to perform logic operations with a chemical device. The use of electric fields and light allows for lower-power operation and creates less heat than logic operations based on electric charge, the researchers said.

The chemical device features molecules that self-assemble into spiral shapes called columnar liquid crystals (CLCs). The orientation of the twisted columns can be altered using electric fields, whereas optical stimuli can be used to induce a second ordering transition.

Performing computational logic with light, University of Tokyo.
Columnar liquid crystals are similar in size to current semiconductor transistors. Courtesy of the Aida Group.

Before a logic operation begins, the researchers sandwich a sample of CLCs between two glass plates covered in electrodes. Polarized light passes through the sample to a detector on the other side.

In the sample’s default state, the CLCs exist in a randomly oriented state that allows the light to reach the detector. When either the electric field or the UV light is switched on and then off, the detected output remains the same as in the default state. However, when the researchers switch both the electric field and the UV light on and then off after about 1 second, the CLCs line up to block the detector from the light.

The researchers said that if the output states of light and dark and the input states of the electric field and UV light are all assigned binary digits to identify them, the process can effectively perform a logical AND function. In an AND function, all inputs to the function must be “1” for the output to be “1.”

Performing computational logic with light, University of Tokyo.
The sample of columnar liquid crystals changes its state in 1 second but can last for hours. Courtesy of the Aida Group.

“The AND function is one of several fundamental logic functions, but the most important one for computation is the NOT-AND, or NAND, function,” said researcher Keiichi Yano. “This is one of several areas for further research.” 


The researchers also intend to increase the speed and density of the CLCs to make them more practical to use. “I’m fascinated by how self-assembling molecules like those we use to make the CLCs give rise to phenomena such as logical functions,” Yano said.

The research was published in Science (http://dx.doi.org/10.1126/science.aan1019). 

For the first time, researchers performed logic operations — the basis of computation — with a chemical device using electric fields and ultraviolet light. The device and the pioneering methods used open up research possibilities including low-power, high-performance computer chips. Courtesy of the  Aida Group.

Photonics Handbook
GLOSSARY
optical communications
The transmission and reception of information by optical devices and sensors.
optoelectronics
A sub-field of photonics that pertains to an electronic device that responds to optical power, emits or modifies optical radiation, or utilizes optical radiation for its internal operation. Any device that functions as an electrical-to-optical or optical-to-electrical transducer. Electro-optic often is used erroneously as a synonym.
Research & TechnologyeducationAsia-PacificUniversity of TokyoRIKENlight sourcesmaterialsopticsSensors & DetectorsCommunicationsoptical communicationsoptoelectronics

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